1. Field of the Invention
The present invention relates to optical filter modules and optical apparatuses using them, and particularly to an optical filter module including an optical filter, an optical system to guide the light to be supplied to the optical filter and the optical system to guide the light supplied from the optical filter, and various kinds of optical apparatuses such as an optical multi/demultiplexer using it or an optical equalizer.
2. Description of the Related Art
In a field of optics, an optical filter module is used, which is comprised of an optical filter to selectively transmit, attenuate, or reflect the light with a specific wavelength, and an optical system to supply the light to the optical filter or guide the light from the optical filter. For example, there known the apparatuses such as an optical multi/demultiplexer which multiplexes a plurality of lights with different wavelengths and demultiplexes the light to a plurality of lights with different wavelengths or a light equalizer which corrects intensity of the light that is not constant to the wavelength to the one that is constant.
FIG. 32 shows an optical multi/demultiplexer 90 as an example of an optical filter module. This optical multi/demultiplexer 90 is provided with a first collimator 100 having 2 optical fibers 101 and 102, and a second collimator 110 having one optical fiber 111, and a wavelength band-pass filter 95 arranged between these collimators 100 and 110.
The first collimator 100 and the second collimator 110 have ceramic fiber holders 104 and 114 to hold the optical fiber. In the fiber holder 104 of the first collimator 100, two through-holes having a circular sectional shape, are formed along its longitudinal direction, and in the fiber holder 114 of the second collimator 110, one through-hole whose sectional shape is circular is formed along its longitudinal direction. The optical fibers are inserted into these through-holes, and held by being fixed by an adhesive agent.
Further, on the first collimator 100 and the second collimator 110, rod lenses 103 and 112 to collimate and converge the light are provided. These rod lenses 103 and 112 are held by inner holders 105 and 115 together with the optical fiber holders 104 and 114, and these inner holders 105 and 115 are fixed in an outside holder 120 by using the adhesive agent or soldering, or a method such as a YAG welding.
A wavelength band-pass filter 95 is closely contacted under the close contact condition to the rod lens 103, and fixed by the adhesive agent 107 coated around the closely contacted surface.
When the light is demultiplexed by such an optical multi/demultiplexer 90, the light incident into one of optical fibers of the first collimator 100 is collimated by the rod lens 103, and reaches the wavelength band-pass filter 95. The light of the wavelength reflected by this wavelength band-pass filter 95 passes through the rod lens 103, and emitted from the other optical fiber of the first collimator 100. On the other hand, the light passes through the wavelength band-pass filter 95 is converged by the rod lens 112 of the second collimator 110 and emitted from the optical fiber 111.
Further, when the light is multiplexed by such an optical multi/demultiplexer 90, the light incident from the optical fiber 111 of the second collimator 110, is multiplexed with the light introduced one of the optical fibers of the first collimator 100, and outputted from the other optical fiber of the first collimator.
However, in such the optical multi/demultiplexer 90 as described above, there is sometimes a case where the adhesive agent 107 before hardening, which is coated on the outer peripheral surface of the rod lens 103 and wavelength band-pass filter 95 penetrates between the closely contacted surfaces of the rod lens 103 and the wavelength band-pass filter 95 by a capillary phenomenon. Further, the closely contacted surface of the wavelength band-pass filter 95 is inclined to the closely contacted surface of the rod lens 103, thereby, a gap is generated between the rod lens 103 and the wavelength band-pass filter 95, and there is a case where the adhesive agent 107 before hardening penetrates from the gap.
When this adhesive agent 107 reaches a central portion of the closely contacted surface including the optical path, the adhesive agent interrupts the optical path and increases the loss of the light. Further, there is also a case where, by the temperature change under the using environment, the adhesive agent 107 penetrated into the closely contacted surfaces is expanded and contracted, and the position dislocation of the wavelength band-pass filter 95 is generated, or the stress is generated by the contact of the optical parts, and the loss of the light is increased.
In order to prevent this, it is considered that, as the adhesive agent 107, the adhesive agent whose viscosity is high is used, and the penetration into between closely contacted surfaces is prevented, however, even when such the adhesive agent is used, it is difficult to perfectly prevent the penetration. Further, in the adhesive agent whose viscosity is high, the control of the coating amount is difficult, and there is also a problem that a dispenser to coat the adhesive agent is high in cost. Further, there is also a problem that, naturally, in the closely contacting of the optical parts, because it is necessary to use the adhesive agent whose thermal expansion property is low, the width of the selection of the adhesive agent having a predetermined viscosity is very narrow.
The present invention is attained for solving the above problems, and an object of the present invention is to provide a optical filter module by which the loss of the light by the adhesive agent penetrated between the closely contacted surfaces of the rod lens and the optical filter can be reduced, and each kind of optical devices such as an optical multi/demultiplexer using it.
In order to attain the above object, the optical filter module in the present invention is provided with an optical filter to selectively transmit, attenuate or reflect the light with a specific wavelength, and the first optical system including the optical fiber to guide the light to be supplied to the optical filter, and the second optical system which is oppositely provided to the first optical system through the optical filter, and which includes the optical fiber to guide the light to be supplied from the optical filter, wherein each of the optical systems has the a lens to optically connect the optical fiber and the optical filter, and the surface including the optical path of the optical filter is closely contacted by the adhesive agent coated on a portion which is not the optical path, under the closely contacted with the end surface including the optical path of any one lens of the first or second optical systems, and a groove portion to stay the adhesive agent penetrated between the closely contacted surfaces on at least one closely contacted surface of the optical filter and the lens, and to interrupt the adhesive agent from invading into the optical path is formed.
Further, the optical filter module of the present invention is provided with an optical filter to selectively transmit, attenuate or reflect the light with a specific wavelength, and the first optical system including the optical fiber to guide the light to be supplied to the optical filter, and the second optical system which is oppositely provided to the first optical system through the optical filter, and which includes the optical fiber to guide the light to be supplied from the optical filter, wherein each of the optical systems has the a lens to optically connect the optical fiber and the optical filter, and on the end surface of one lens of the optical system, a convex surface including the optical path and a flat portion protruded to the outside of the optical path direction more than the convex surface from the periphery of the convex surface are formed, and the surface including the optical path of the optical filter is closely contacted to the lens by the adhesive agent coated on a portion which is not the optical path, under closely contacted condition with the flat portion of the lens.
According to the optical filter module according to the present invention, because the adhesive agent before hardening penetrated between the closely contacted surfaces of the optical filter and the rod lens is stayed in the groove portion or between the convex surface and the flat portion, it is prevented that the adhesive agent reaches a central portion as the optical path and interrupts the optical path.
Further, when the adhesive agent penetrated between the closely contacted surfaces is expanded and contracted by the temperature change under the using environment, the expanded portion and contracted portion can be absorbed by the groove portion or between the convex surface and the flat portion. Accordingly, the optical filter module having the small optical loss can be provided.